1. Field of the Invention
This invention relates to novel mutants of the first Kunitz domain (IC) of the human lipoprotein-associated coagulation inhibitor LACI, which inhibit plasmin. The invention also relates to other modified Kunitz domains that inhibit plasmin and to other plasmin inhibitors.
2. Description of the Background Art
The agent mainly responsible for fibrinolysis is plasmin, the activated form of plasminogen. Many substances can activate plasminogen, including activated Hageman factor, streptokinase, urokinase (uPA), tissue-type plasminogen activator (tPA), and plasma kallikrein (pKA). pKA is both an activator of the zymogen form of urokinase and a direct plasminogen activator.
Plasmin is undetectable in normal circulating blood, but plasminogen, the zymogen, is present at about 3 xcexcM. An additional, unmeasured amount of plasminogen is bound to fibrin and other components of the extracellular matrix and cell surfaces. Normal blood contains the physiological inhibitor of plasmin, xcex12-plasmin inhibitor (xcex12-PI), at about 2 xcexcM Plasmin and xcex12-PI form a 1:1 complex Matrix or cell bound-plasmin is relatively inaccessible to inhibition by xcex12-PI. Thus, activation of plasmin can exceed the neutralizing capacity of xcex12-PI causing a profibrinolytic state.
Plasmin, once formed:
i. degrades fibrin clots, sometimes prematurely;
ii. digests fibrinogen (the building material of clots) impairing hemostasis by causing formation of friable, easily lysed clots from the degradation products, and inhibition of platelet adhesion/aggregation by the fibrinogen degradation products;
iii. interacts directly with platelets to cleave glycoproteins Ib and IIb/IIIa preventing adhesion to injured endothelium in areas of high shear blood flow and impairing the aggregation response needed for platelet plug formation (ADEL86);
iv. proteolytically inactivates enzymes in the extrinsic coagulation pathway further promoting a prolytic state.
Robbins (ROBB87) reviewed the plasminogen-plasmin system in detail. ROBB87 and references cited therein are hereby incorporated by reference.
Inappropriate fibrinolysis and fibrinogenolysis leading to excessive bleeding is a frequent complication of surgical procedures that require extracorporeal circulation, such as cardiopulmonary bypass, and is also encountered in thrombolytic therapy and organ transplantation, particularly liver. Other clinical conditions characterized by high incidence of bleeding diathesis include liver cirrhosis, amyloidosis, acute promyelocytic leukemia, and solid tumors. Restoration of hemostasis requires infusion of plasma and/or plasma products, which risks immunological reaction and exposure to pathogens, e.g. hepatitis virus and WV.
Very high blood loss can resist resolution even with massive infusion. When judged life-threatening, the hemorrhage is treated with antifibrinolytics such as E-amino caproic acid (See HOOV93) (EACA), tranexamic acid, or aprotinin (NEUH89). Aprotinin is also known as Trasylol(trademark) and as Bovine Pancreatic Trypsin Inhibitor (BPTf). Hereinafter, aprotinin will be referred to as xe2x80x9cBPTIxe2x80x9d. EACA and tranexamic acid only prevent plasmin from binding fibrin by binding the kringles, thus leaving plasmin as a free protease in plasma. BPTI is a direct inhibitor of plasmin and is the most effective of these agents. Due to the potential for thrombotic complications, renal toxicity and, in the case of BPTI, immunogenicity, these agents are used with caution and usually reserved as a xe2x80x9clast resortxe2x80x9d (PUTT89). All three of the antifibrinolytic agents lack target specificity and affinity and interact with tissues and organs through uncharacterized metabolic pathways. The large doses required due to low affinity, side effects due to lack of specificity and potential for immune reaction and organ/tissue toxicity augment against use of these antifibrinolytics prophylactically to prevent bleeding or as a routine postoperative therapy to avoid or reduce transfusion therapy. Thus, there is a need for a safe antifibrinolytic. The essential attributes of such an agent are:
i Neutralization of relevant target fibrinolytic enzyme(s);
ii. High affinity binding to target enzymes to minimize dose;
iii. High specificity for target, to reduce side effects; and
iv. High degree of similarity to human protein to minimize potential immunogenicity and organ/tissue toxicity.
All of the fibrinolytic enzymes that are candidate targets for inhibition by an efficacious antifibrinolytic are chymotrypin-homologous serine proteases.
Excessive bleeding can result from deficient coagulation activity, elevated fibrinolytic activity, or a combination of the two conditions. In most bleeding diatheses one must control the activity of plasmin The clinically beneficial effect of BPTI in reducing blood loss is thought to result from its inhibition of plasmin (KDxcx9c0.3 nM) or of plasma kallikrein (KDxcx9c100 nM) or both enzymes.
GARD93 reviews currently-used thrombolytics, saying that, although thrombolytic agents (e.g. tPA) do open blood vessels, excessive bleeding is a serious safety issue. Although tPA and streptokinase have short plasma half lives, the plasmin they activate remains in the system for a long time and, as stated, the system is potentially deficient in plasmin inhibitors. Thus, excessive activation of plasminogen can lead to a dangerous inability to clot and injurious or fatal hemorrhage. A potent, highly specific plasmin inhibitor would be useful in such cases.
BPTI is a potent plasmin inhibitor; it has been found, however, that it is sufficiently antigenic that second uses require skin testing. Furthermore, the doses of BPTI required to control bleeding are quite high and the mechanism of action is not clear. Some say that BPTI acts on plasmin while others say that it acts by inhibiting plasma kallikrein. FRAE89 reports that doses of about 840 mg of BPTI to 80 open-heart surgery patients reduced blood loss by almost half and the mean amount transfused was decreased by 74%. Miles Inc. has recently introduced Trasylol in USA for reduction of bleeding in surgery (See Miles product brochure on Trasylol, which is hereby incorporated by reference.) LOHM93 suggests that plasmin inhibitors may be useful in controlling bleeding in surgery of the eye. SHER89 reports that BPTI may be useful in limiting bleeding in colonic surgery.
A plasmin inhibitor that is approximately as potent as BPTI or more potent but that is almost identical to a human protein domain offers similar therapeutic potential but poses less potential for antigenicity.
Plasmin is the key enzyme in angiogenesis. 0RE194 reports that a 38 kDa fragment of plasmin (lacking the catalytic domain) is a potent inhibitor of metastasis, indicating that inhibition of plasmin could be useful in blocking metastasis of tumors (FIDL94). See also ELLI92. ELLI92, OREI94 and FIDL94 and the references cited there are hereby incorporated by reference.
Plasmin is a serine protease derived from plasminogen. The catalytic domain of plasmin (or xe2x80x9cCatDomxe2x80x9d ) cuts peptide bonds, particularly after arginine residues and to a lesser extent after lysines and is highly homologous to trypsin, chymotrypsin, kallikrein, and many other serine proteases. Most of the specificity of plasmin derives from the kringles"" binding of fibrin (LUCA83, VARA83, VARA84). On activation, the bond between ARG561-Val562 is cut, allowing the newly free amino terminus to form a salt bridge. The kringles remain, nevertheless, attached to the CatDom through two disulfides (COLM87, ROBB87).
BPTI has been reported to inhibit plasmin with KD of about 300 pM (SCHN86). AUER88 reports that BPTI(R15) has Ki for plasmin of about 13 nM, suggesting that R15 is substantially worse than K5 for plasmin binding. SCHN86 reports that BPTI in which the residues C14 and C38 have been converted to Alanine has Ki for plasmin of about 4.5 nM. KIDO88 reports that APP-I has Ki for plasmin of about 75 pM (7.5xc3x9710xe2x88x9211 M), the most potent inhibitor of human plasmin reported so far. DENN94a reports, however, that APP-I inhibits plasmin with Ki=225 nM (2.25xc3x9710xe2x88x927 M). Our second and third libraries were designed under the assumption that APP-I is a potent plasmin binder. The selection process did not select APP-I residues at most locations and the report of DENN94a explains why this happened.
With recombinant DNA techniques, it is possible to obtain a novel protein by expressing a mutated gene encoding a mutant of the native protein gene. Several strategies for picking mutations are known. In one strategy, some residues are kept constant, others are randomly mutated, and still others are mutated in a predetermined manner. This is called xe2x80x9cvariegationxe2x80x9d and is defined in Ladner et al. U.S. Pat. No. 5,223,409, which is incorporated by reference.
DENN94a and DENN94b report selections of Kunitz domains based on APP-I for binding to the complex of Tissue Factor with Factor VIIa. They did not use LACI-KI1 as parental and did not use plasmin as a target. The highest affinity binder they obtained had KD for their target of about 2 nM. Our first-round selectants have affinity in this range, but our second round selectants are about 25-fold better than this.
Proteins taken from a particular species are assumed to be less likely to cause an immune response when injected into individuals of that species. Murine antibodies are highly antigenic in humans. xe2x80x9cChimericxe2x80x9d antibodies having human constant domains and murine variable domains are decidedly less antigenic. So called xe2x80x9chumanizedxe2x80x9d antibodies have human constant domains and variable domains in which the CDRs are taken from murine antibodies while the framework of the variable domains are of human origin. xe2x80x9cHumanizedxe2x80x9d antibodies are much less antigenic than are xe2x80x9cchimericxe2x80x9d antibodies. In a xe2x80x9chumanizedxe2x80x9d antibody, fifty to sixty residues of the protein are of non-human origin. The proteins of this invention comprise, in most cases, only about sixty amino acids and usually there are ten or fewer differences between the engineered protein and the parental protein. Although humans do develop antibodies even to human proteins, such as human insulin, such antibodies tend to bind weakly and the often do not prevent the injected protein from displaying its intended biological function. Using a protein from the species to be treated does not guarantee that there will be no immune response. Nevertheless, picking a protein very close in sequence to a human protein greatly reduces the risk of strong immune response in humans.
Kunitz domains are highly stable and can be produced efficiently in yeast or other host organisms. At least ten human Kunitz domains have been reported. Although APP-I was thought at one time to be a potent plasmin inhibitor, there are, actually, no human Kunitz domains that inhibit plasmin as well as does BPTI. Thus, it is a goal of the present invention to provide sequences of Kunitz domain that are both potent inhibitors of plasmin and close in sequence to human Kunitz domains.
The use of site-specific mutagenesis, whether nonrandom or random, to obtain mutant binding proteins of improved activity is known in the art, but success is not assured.
This invention relates to mutants of BPTI-homologous Kunitz domains that potently inhibit human plasmin. In particular, this invention relates to mutants of one domain of human LACI which are likely to be non-immunogenic to humans, and which inhibit plasmin with KD, preferably, of about 5 nM or less, more preferably of about 300 pM or less, and most preferably about 100 pM or less. The invention also relates to the therapeutic and diagnostic use of these novel proteins.
Plasmin-inhibiting proteins are useful for the prevention or treatment of clinical conditions caused or exacerbated by plasmin, including inappropriate fibrinolysis or fibrinogenolysis, excessive bleeding associated with thrombolytics, post-operative bleeding, and inappropriate androgenesis. Plasmin-binding mutants, whether or not inhibitory, are useful for assaying plasmin in samples, in vitro, for imaging areas of plasmin activity, in vivo, and for purification of plasmin.
Preferred mutants QS4 and NS4 were selected from a library that allowed about 50 million proteins having variability at positions 13, 16, 17, 18, 19, 31, 32, 34, and 39. These proteins have an amino-acid sequence nearly identical to a human protein but inhibit plasmin with Ki of about 2 nM (i.e. about 6-fold less potent than BPTI, but 100-fold better than APP-I).
An especially preferred protein, SPI 11, was selected from a library allowing variability at positions 10, 11, 13, 15, 16, 17, 18, 19, and 21 and has an affinity for plasmin which is less than 100 pM (i.e. about 3-fold superior to BPTI in binding), and yet is much more similar in sequence to LACI, a human protein, than to the BPTI, a bovine protein. Other LACI-K1 mutants selected from this library and thought to have very high affinity for plasmin include SPI15, SPI08, and SPI23. An additional library allowing variation at positions 10, 11, 13, 15, 16, 17, 18, 19, 21, 31, 32,34,35, and 39 has been screened and a consensus sequence (SPIcon1) found. Variants shown to be better than QS4, and thus more preferred, include SPI51 and SPI47. Sequences that are likely to have very high affinity for plasmin yet retain an essentially human amino-acid sequence have been identified and include sequences SPI60, SPI59, SPI42, SPI55, SPI56, SPI52, SPI46, SPI49, SPI53, SPI41, and SPI57. The amino-acid sequence information that confers high affinity for the active site of plasmin can be transferred to other Kunitz domains, particularly to Kunitz domains of human origin; designs of several such proteins are disclosed.
The preferred plasmin inhibitors of the present invention fullfill one or more of the following desiderata:
1) the Ki for plasmin is at most 20 nM, preferably not more than about 5 nM, more preferably not more than about 300 pM, and most preferably, not more than about 100 pm,
2) the inhibitor comprises a Kunitz domain meeting the requirements shown in Table 14 with residues number by reference to BPTI,
3) at the Kunitz domain positions 12-21 and 32-39 one of the amino-acid types listed for that position in Table 15, and
4) the inhibitor is more similar in aminoacid sequence to a reference sequence selected from the group SPI11, SPI15, SPI08, SPI23, SPI51, SPI47, QS4, NS4, Human LACI-K2, Human LACI-K3, Human collagen xcex13 KuDom, Human TFPI-2 DOMAIN 1, Human TFPI-2 DOMAIN 2, Human TFPI-2 DOMAIN 3, HUMAN ITI-K1, Human ITI-K2, HUMAN PROTEASE NEXIN-II Human APP-I DPI-11.1, DPI-1.1.2, DPI-1.1.3, DPI-1.2.1, DPI-1.3.1, DPI-2.1, DPI-3.1.1, DPI-3.2.1, DPI-3.3.1, DPI4.1.1, DPI4.2.1, DPI-4.2.2, DPI-4.2.3, DPI-4.2.4, DPI-4.2.5, DPI-5.1, DPI-5.2, DPI-6.1, DPI-6.2 than is the amino acid sequence of said Kunitz domain to the sequence of BPTI.
Herein, affinities are stated as KD (KD(A,B)=[A][B]/[Axe2x88x92B]). A numerically smaller KD reflects higher affinity. For the purposes of this invention, a xe2x80x9cplasmin inhibiting proteinxe2x80x9d is one that binds and inhibits plasmin with Ki of about 20 nM or less. xe2x80x9cInhibitionxe2x80x9d refers to blocking the catalytic activity of plasmin and so is measurable in vitro in assays using chromogenic or fluorogenic substrates or in assays involving macromolecules.
Amino-acid residues are discussed in three ways: full name of the amino acid, standard three-letter code, and standard single-letter code. Table use only the one-letter code. The text uses full names and three-letter code where clarity requires.
For the purposes of this invention, xe2x80x9csubstantially homologousxe2x80x9d sequences are at least 51%, more preferably at least 80%, identical, over any specified regions. Herein, sequences that are identical are understood to be xe2x80x9csubstantially homologousxe2x80x9d. Sequences would still be xe2x80x9csubstantially homologousxe2x80x9d if within one region of at least 20 amino acids they are sufficiently similar (51% or more) but outside the region of comparison they differed totally. An insertion of one amino acid in one sequence relative to the other counts as one mismatch. Most preferably, no more than six residues, other than at termini, are different. Preferably, the divergence in sequence, particularly in the specified regions, is in the form of xe2x80x9cconservative modificationsxe2x80x9d.
xe2x80x9cConservative modificationsxe2x80x9d are defined as
(a) conservative substitutions of amino acids as defined in Table 9; and
(b) single or multiple insertions or deletions of amino acids at termini, at domain boundaries, in loops, or in other segments of relatively high mobility.
Preferably, except at termini, no more than about six amino acids are inserted or deleted at any locus, and the modifications are outside regions known to contain important binding sites.
Herein, xe2x80x9cKunitz domainxe2x80x9d and xe2x80x9cKuDomxe2x80x9d are used interchangeably to mean a homologue of BPTI (not of the Kunitz soya-bean trypsin inhibitor). A KuDom is a domain of a protein having at least 51 amino acids (and up to about 61 amino acids) containing at least two, and preferably three, disulfides. Herein, the residues of all Kunitz domains are numbered by reference to BPTI (i.e. residues 1-58). Thus the first cysteine residue is residue 5 and the last cysteine is 55. An amino-acid sequence shall, for the purposes of this invention, be deemed a Kunitz domain if it can be aligned, with three or fewer mismatches, to the sequence shown in Table 14. An insertion or deletion of one residue shall count as one mismatch In Table 14, xe2x80x9cxxe2x80x9d matches any amino acid and xe2x80x9cXxe2x80x9d matches the types listed for that position. Disulfides bonds link at least two of: 5 to 55, 14 to 38, and 30 to 51. The number of disulfides may be reduced by one, but none of the standard cysteines shall be left unpaired. Thus, if one cysteine is changed, then a compensating cysteine is added in a suitable location or the matching cysteine is also replaced by a non-cysteine (the latter being generally preferred). For example, Drosophila funebris male accessory gland protease inhibitor has no cysteine at position 5, but has a cysteine at position xe2x88x921 Oust before position 1); presumably this forms a disulfide to CYS55. If Cyst14 and Cys38 are replaced, the requirement of Gly,12, (Gly or Ser)37, and Gly36 are dropped. From zero to many residues, including additional domains (including other KuDoms), can be attached to either end of a Kunitz domain.
Protease inhibitors, such as Kunitz domains, function by binding into the active site of the protease so that a peptide bond (the xe2x80x9cscissile bondxe2x80x9d) is: 1) not cleaved, 2) cleaved very slowly, or 3) cleaved to no effect because the structure of the inhibitor prevents release or separation of the cleaved segments. In Kunitz domains, disulfide bonds act to hold the protein together even if exposed peptide bonds are cleaved. From the residue on the amino side of the scissile bond, and moving away from the bond, residues are conventionally called P1, P2, P3, etc. Residues that follow the scissile bond are called P1xe2x80x2, P2xe2x80x2, P3xe2x80x2, etc. (SCHE67, SCHE68). It is generally accepted that each serine protease has sites (comprising several residues) S1, S2, etc. that receive the side groups and main-chain atoms of residues P1, P2, etc. of the substrate or inhibitor and sites S 1xe2x80x2, S2xe2x80x2, etc. that receive the side groups and main-chain atoms of P1xe2x80x2, P2xe2x80x2, etc. of the substrate or inhibitor. It is the interactions between the S sites and the P side groups and main chain atoms that give the protease specificity with respect to substrates and the inhibitors specificity with respect to proteases. Because the fragment having the new amino terminus leaves the protease first, many worker designing small molecule protease inhibitors have concentrated on compounds that bind sites S1, S2, S3, etc.
LASK80 reviews protein protease inhibitors. Some inhibitors have several reactive sites on one polypeptide chain, and these domains usually have different sequences, specificities, and even topologies. It is known that substituting amino acids in the P5 to P5xe2x80x2 region influences the specificity of an inhibitor. Previously, attention has been focused on the P1 residue and those very close to it because these can change the specificity from one enzyme class to another. LASK80 suggests that among KuDoms, inhibitors with P1=Lys or Arg inhibit trypsin, those with P1=Tyr, Phe, Trp, Leu and Met inhibit chymotrypsin, and those with P1=Ala or Ser are likely to inhibit elastase. Among the Kazal inhibitors, LASK80 continues, inhibitors with P1=Leu or Met are strong inhibitors of elastase, and in the Bowman-Kirk family elastase is inhibited with P1=Ala, but not with P1=Leu. Such limited changes do not provide inhibitors of truly high affinity (i.e. better than 1 to 10 nM).
Kunitz domains are defined above. The 3D structure (at high resolution) of BPTI (the archetypal Kunitz domain) is known. One of the X-ray structures is deposited in the Brookhaven Protein Data Bank as xe2x80x9c6PTIxe2x80x9d]. The 3D structure of some BPTI homologues (EIGE90, HYNE90) are known. At least seventy KuDom sequences are known. Known human homologues include three KuDoms of LACI (WUNT88, GIRA89, NOVO89), two KuDoms of Inter-xcex1-Trypsin Inhibitor, APP-I (KIDO88), a KuDom from collagen, and three KuDoms of TFPI-2 (SPRE94). LACI
Lipoprotein-associated coagulation inhibitor (LACI) is a human serum phosphoglycoprotein with a molecular weight of 39 kDa (amino-acid sequence in Table 1) containing three KuDoms. We refer hereinafter to the protein as LACI and to the Kunitz domains thereof as LACI-K1 (residues 50 to 107 ), LACI-K2 (residues 121 to 178), and LAC[-K3 (213 to 270). The cDNA sequence of LACI is reported in WUNT88, GIRA89 reports mutational studies in which the P1 residues of each of the three KuDoms were altered. LACI-K1 inhibits Factor VIIa (F.VIIa) when F.VIIa is complexed to tissue factor and LACI-K2 inhibits Factor Xa. It is not known whether LACI-K3 inhibits anything Neither LACI nor any of the KuDoms of LACI is a potent plasmin inhibitor.
KuDoms of this invention are substantially homologous with LACI-K 1, but differ in ways that confer strong plasmin inhibitory activity discussed below. Other KuDoms of this invention are homologous to other naturally-occurring KuDoms, particularly to other human KuDoms. For use in humans, the proteins of this invention are designed to be more similar in sequence to a human KuDom than to BPTI, to reduce the risk of causing an immune response.
Applicants have screened a first library of LACI-K1 for mutants having high affinity for human plasmin and obtained the sequences shown in Table 2 and Table 3. These sequences may be summarized as shown in Table 16, where xe2x80x9cpreferred residuesxe2x80x9d are those appearing in at least one of the 32 variants identified as binding plasmin. The preferences at residues 13, 16, 17, 18 and 19 are strong, as shown in Table 17. Although the range of types allowed at 31 and 32 is limited, the selection indicates that an acidic group at 31 and a neutral group at 32 is preferred. At residue 17, Arg was preferred; Lys, another positively charged amino acid, was not in the library, and may be a suitable substitute for Arg. Many amino-acid type at positions 34 and 39 are consistent with high-affinity plasmin binding, but some types may hinder binding.
It should be appreciated that Applicants have not sequenced all the positive isolates of this or other libraries herein disclosed, and that some of the possible proteins may not have been present in detectable amounts.
Applicants have prepared one of the selected proteins, QS4, shown in Table 2. QS4 inhibits plasmin with a Ki of about 2 nM. Although this level of inhibition is less than that of BPTI, QS4 is a preferred molecule for use in humans because it has less potential for immunogenicity. Other proteins shown in Table 2 and Table 3 are very likely to be potent inhibitors of plasmin and are likely to pose little threat of antigenicity.
Applicants have prepared a second library of LACI-K1 derivatives shown in Table 5 and allowing variation at residues 10, 11, 13, 15, 16, 17, 18, 19, and 21. This was screened for binding to plasmin and the proteins shown in Table 6 were obtained.
xe2x80x9cConsensusxe2x80x9d in Table 6 is E10TGPCRARFERW21 (SEQ ID NO:88), where the seven underscored residues differ from LACI-K1. Only acidic amino acids (Glu: 17 or Asp: 15) were seen at position 10; Lys and Asn are not acceptable. As Glu and Asp appeared with almost equal frequency, they probably contribute equally to binding. Acidic residues were not seen at position 11. Thr was most common (11/32) with Ser appearing often (9/32); Gly appeared 8 times. At 13, Pro was strongly preferred (24/32) with Ala second at 5/32. At 15, Arg was strongly preferred (25/32), but a few (7/32) isolates have Lys. Note the BPTI(R15) is a worse plasmin inhibitor than is BPTI. At 16, Ala was preferred (22/32), but Gly appeared fairly often (10/32). At 17, Arg was most common (15/32), with Lys coming second (9/32). At residues 17 and 18, APP-I has Met and Ile. At 18, we allowed Ile or Phe. Only four isolates have Ile at 18 and none of these have Met at 17. This was surprising in view of KIDO88, but quite understandable in view of DENN94a. This collection of isolates has a broad distribution at 19: (Glu:8, Pro:7, Asp:4, Ala:3, His:3, Gly:2, Gln:2, Asn:1, Ser:1, and Arg:1), but acidic side groups are strongly preferred over basic ones. At 21, the distribution was (Trp: 16, Phe: 14, Leu:2, Cys:0); BPTI has Tyr at 21.
The binding of clonally pure phage that display one or another of these proteins was compared to the binding of BPTI phage (Table 6). Applicants have determined the Kj of protein SPI11 and found it to be about 88 pM which is substantially superior to BPTI.
Applicants used a pool of phage of the second library (varied at residues 10, 11, 13, 15, 16, 17, 18, 19, and 21) that had been selected twice for plasmin binding as a source of DNA into which variegation was introduced at residues 31, 32, 34, 35, and 39 as shown in Table 7.
This library was screened for three rounds for binding to plasmin and the isolates shown in Table 8 were obtained. The distribution of amino-acid types is shown in Table 18 where xe2x80x9cxxe2x80x9d means the amino-acid type was not allowed and xe2x80x9c*xe2x80x9d indicates the wild-type for LACI-K1.
These sequences gave a consensus in the 10-21 and 31-40 region of E10TGPCRAKFDRW21 . . . E31AFVYGGC GG40 (residues 10-21 and 31-40 of SEQ ID NO:45; SPIcon1 in Table 4). The ten underscored amino acids differ from LACI-K 1. At eight varied positions, a second type was quite common: Asp at 10, Ala at 11, Glu at 19, Phe at 21, Thr at 31, Pro or Ser at 32, Leu or Ile at 34, and Glu at 39. At position 17, the highly potent inhibitor SPI11 has R. Thus, the sequence D10TGPCRARFDRF21 . . . E31AFIYGGCEG40 (residues 10-21 and 31-40 of SEQ ID NO:61; DPI-1.1.1 in Table 4) differs from LACI-K1 by only six residues, matches the selected sequences at the residues having strong consensus, and has preferred substitutions at positions 10, 17, 21, 34, and 39. DPI-1.1.1 is expected to have a very high affinity for plasmin and little potential for immunogenicity in humans.
Preliminary testing of proteins SPI11, BPTI, SPI23, SPI51, SPI47, QS4, SPI22, SPI54, and SPI43 for plasmin inhibitory activity placed them in the order given. SPI11 is significantly more potent than BPTI with Ki of about 88 pM. SPI23 and SPI51 are very similar in activity and only slightly less potent than BPTI. SPI47 is less potent than SPI51 but better than QS4. SPI22 is weaker than QS4. SPI54 and SPI43 are not so potent as QS4, Ki probably  greater than 4 nM.
A KuDom that is highly homologous at residues 5-55 to any one of the sequences SPI11, SPI15, SPI08, SPI23, SPI51, SPI47, QS4, and NS4, as shown in Table 4, is likely to be a potent inhibitor (KD greater than 5 nM) of plasmin and have a low potential for antigenicity in humans. More preferably, to have high affinity for plasmin, a KuDom would have a sequence that is identical at residues 10-21 and 31-39 and has five or fewer differences at residues 5-9, 22-30, and 40-55 as compared to any of the sequences SPI11, SPI15, SPI08, SPI23, SPI51, SPI47, QS4, and NS4.
Using the selected sequences and the binding data of selected and natural KuDoms, we can write a recipe for a high-affinity plasmin-inhibiting KuDom that can be applied to other human KuDom parentals. First, the KuDom must meet the requirements in Table 14. The substitutions shown in Table 15 are likely to confer high-affinity plasmin inhibitory activity on any KuDom. Thus a protein that contains a sequence that is a KuDom, as shown in Table 14, and that contains at each of the position 12-21 and 32-39 an amino-acid type shown in Table 15 for that position is likely to be a potent inhibitor of human plasmin. More preferably, the protein would have an amino-acid type shown in Table 15 for all of the positions listed in Table 15. To reduce the potential for immune response, one should use one or another human KuDom as parental protein to give the sequence outside the binding region.
It is likely that a protein that comprises an amino-acid sequence that is substantially homologous to SPI11 from residue 5 through residue 55 (as shown in Table 4) and is identical to SPI11 at positions 13-19, 31, 32, 34, and 39 will inhibit human plasmin with a Ki of 5 nM or less. SPI11 differs from LACI-K1 at 7 positions. It is not clear that these substitutions are equally important in fostering plasmin binding and inhibition. There are seven molecules in which one of the substituted positions of SPI11 is changed to the residue found in LACI-K1 (i.e. xe2x80x9crevertedxe2x80x9d), 21 in which two of the residues are reverted, 35 in which three residues are reverted, 35 in which four are reverted, 21 in which five are reverted, and seven in which six are reverted. It is expected that those with more residues reverted will have less affinity for plasmin but also less potential for immunogenicity. A person skilled in the art can pick a protein of sufficient potency and low immunogenicity from this collection of 126. It is also possible that substitutions in SPI11 by amino acids that differ from LACI-K1 can reduce the immunogenicity without reducing the affinity for plasmin to a degree that makes the protein unsuitable for use as a drug.
Hereinafter, xe2x80x9cDPIxe2x80x9d will mean a xe2x80x9cDesigned Plasmin Inhibitorxe2x80x9d that are KuDoms that incorporate amino-acid sequence information from the SPI series of molecules, especially SPI11. Sequences of several DPIs and their parental proteins are given in Table 4.
Sequences DPI-1.1.1, DPI-1.1.2, DPI-1.1.3 , DPI-1.1.4, DPI-1.1.5, and DPI-1.1.6 (in Table 4) differ from LACI-K1 by 6, 5, 5, 4, 3, and 2 amino acids respectively and represent a series in which affinity for plasmin may decrease slowly while similarity to a human sequence increases so as to reduce likelihood of immunogenicity. The selections from each of the libraries show that M18F is a key substitution and that either I17K or I17R is very important. Selections from the second and third library indicate that Arg is strongly preferred at 15, that an acid side group at 11 is disadvantageous to binding. The highly potent inhibitor SPI 11 differs from the consensus by having R17, as does BPTI. DPI-1.1.1 carries the mutations D11T, K15R, I17R, M18F, K19D, and E32A, and is likely to be highly potent as a plasmin inhibitor. DPI-1.1.2 carries D11T, K15R, I17R, M18F, and K19D, and is likely to be highly potent. DPI-1.1.3 carries the mutations D11A, K15R, I17R, M18F, and K19D relative to LACI-K1. DPI-1.1.3 differs from DPI-1.1.2 by having A11 instead of T11; both proteins are likely to be very potent plasmin inhibitors. DPI-1.1.4 carries the mutations I17R, M18F, K19D, and E32A and should be quite potent. As DPI-1.1.4 has fewer of the SPI1 mutations, it may be less potent, but is also less likely to be immunogenic. DPI-1.1.5 caries the mutations I17R, M18F, and K19D. This protein is likely to be a good inhibitor and is less likely to be immunogenic. DPI-1.1.6 carries only the mutations I17R and M18F but should inhibit plasmin.
Protein DPI-1.2.1 is based on human LACI-K2 and shown in Table 4. The mutations P11T, I13P, Y17R, I18F, T19D, R32E, K34I, and L39E are likely to confer high affinity for plasmin. Some of these substitutions may not be necessary; in particular, P11T and T19D may not be necessary. Other mutations that might improve the plasmin affinity include E9A, D10E, G16A, Y21W, Y21F, R32T, K34V, and L39G.
Protein DPI-1.3.1 (Table 4) is based on human LACI-K3 The mutations R11T, L13P, N17R, E18F, N19D, R31E, P32E, K34I, and S36G are intended to confer high affinity for plasmin. Some of these substitutions may not be necessary; in particular, N19D and P32E may not be necessary. Other changes that might improve KD include D10E, N 17K, F21W and G39E.
Protein DPI-2.1 (Table 4) is a based on the human collagen xcex13 KuDom. The mutations E11T, T13P, D16A, F17R, I18F, L19D, A31E, R32E, and W34 are likely to confer high affinity for plasmin. Some of these substitutions may not be necessary; in particular, L19D and A31E may not be necessary. Other mutations that might improve the plasmin affinity include K9A, D10E, D16G, K20R R32T, W34V, and G39E.
DPI-3.1.1 (Table 4) is derived from Human TFPI-2 domain 1. The exchanges Y11T, L17R, L18F, L19D, and R31 E are likely to confer high affinity for plasmin. The mutation L19D may not be needed. Other mutations that might foster plasmin binding include Y21W, Y21F, Q32E, L34I, L34V, and E39G.
DPI-3.2.1 (Table 4) is derived from Human TFPI-2 domain 2. This parental domain contains insertions after residue 9 (one residue) and 42 (two residues). The mutations (V9SVDDQC14 replaced by V9ETGPC14), E15R, S17K, T18F, K32T, F34V, and (H39RNRIENR44 replaced by (E39GNRNR44) are likely to confer affinity for plasmin. Because of the need to change the number of amino acids, DPI-3.2.1 has a higher potential for immunogenicity than do other modified human KuDoms.
DPI-3.3.1 (Table 4) is derived from human TTPI-2, domain 3. The substitutions E11T, L13P, S15R, N17R, V18F, T34I, and T36G are likely to confer high affinity for plasmin. The mutations E11T, L13P, and T34I may not be necessary. Other mutations that might foster plasmin binding include D10E, T19D, Y21W, and G39E.
DPI-4.I.I(Table4) is from human ITI-K1 by assertion of S10E, M15R, M17K, T18F, Q34V, and M39G. The mutations M39G and Q34V may not be necessary. Other mutations that should foster plasmin binding include: A11T, G16A, M17R, S19D, Y21W, and Y21 F.
DPI4.2. (Table 4) is from human ITI-K2 through the mutations V10D, R11T, F17R, I18F, and P34V. The mutation P34V might not be necessary. Other mutation that should foster plasmin binding include: V10E, Q19D, L20R, W21F, P34I, and Q39E. DPI-4.2.2is an especially preferred protein as it has only three mutations: R11T, F17R, and I18F. DPI-4.2.3 is an especially preferred protein as it has only four mutations: R11T, F17R, I18F, and L20R. DPI-4.2.4 is an especially preferred protein as it has only five mutations: R11T,F17R, I18F, L20R, and P34V. DPI-4.2.5 carries the muations V10E, R11T, F17R, I18F, L20R, V31E, L32T, P34V, and Q39G and is highly likely to inhibit plasmin very potently. Each of the proteins DPI-4.2 1, DPI-4.2.2, DPI-4.2.3, DPI-4.2.4, and DPI-4.2.5 is very likely to be a highly potent inhibitor of plasmin.
Before DENN94a, it was thought that APP-I was a very potent plasmin inhibitor. Thus, it was surprising to select proteins from a library that was designed to allow the APP-I residues at positions 10-21 which differed strongly from APP-I. Nevertheless, APP-I can be converted into a potent plasmin inhibitor. DPI-S. I is derived from human APP-1 (also known as Protease Nexin-II) by mutations M17R and I18F and is likely to be a much better plasmin inhibitor than is APP-1 itself. DPI-5.2 carries the further mutations S19D, A31 E, and F34I which may foster higher affinity for plasmin.
DPI6.1is derived from the BKI B9 KuDom (NORR93) by the five substitutions: K11T, Q15R, T16A, M17R, and M18F. DPI-6.1 is likely to be a potent plasmin inhibitor. DPI-6.2 carries the additional mutations T19D and A34V which should foster plasmin binding.
Although BPTI is the best naturally-occurring KuDom plasmin inhibitors known, it could be improved. DPI-7.1 is derived from BPTI by the mutation I18F which is likely to increase the affinity for plasmin. DPI-7.2 carries the further mutation K15R which should increase plasmin binding. DPI-7.3 carries the added mutation R39G. DPI-7.4 carries the mutations Y10D, K15R, I18F, I19D, Q31E, and R39G and should have a very high affinity for plasmin.
KuDoms are quite small; if this should cause a pharmacological problem, such as excessively quick elimination from circulation, two or more such domains may be joined. A preferred linker is a sequence of one or more amino acids. A preferred linker is one found between repeated domains of a human protein, especially the linkers found in human BPTI homologues, one of which has two domains (BALD85, ALBR83b) and another of which has three (WUNT88). Peptide linkers have the advantage that the entire protein may then be expressed by recombinant DNA techniques. It is also possible to use a nonpeptidyl linker, such as one of those commonly used to form immunogenic conjugates. An alternative means of increasing the serum residence of a BPTI-like KuDom is to link it to polyethyleneglycol, so called PEGylation (DAVI79).
Because we have made a large part of the surface of the KuDom SPI11 complementary to the surface of plasmin, R15 is not essential for specific binding to plasmin. Many of the enzymes in the clotting and fibrinolytic pathways cut preferentially after Arg or Lys. Not having a basic residue at the P1 position may give rise to greater specificity. The variant SPI11-R15A (shown in Table 11), having an ALA at P1, is likely to be a good plasmin inhibitor and may have higher specificity for plasmin relative to other proteases than does SPI11. The affinity of SPI11-R15A for plasmin is likely to be less than the affinity of SPI1 for plasmin, but the loss of affinity for other Arg/Lys-preferring enzymes is likely to be greater and, in many applications, specificity is more important than affinity. Other mutants that are likely to have good affinity and very high specificity include SPI11-R15G and SPI11-R15N-E32A. This approach could be applied to other high-affinity plasmin inhibitors.
Variation of SPI 11 as shown in Table 12 and selection of binders is likely to produce a Kunitz domain having affinity for plasmin that is higher than SPI11. This fourth library allows variegation of the 14-38 disulfide. The two segments of DNA shown are synthesized and used with primers in a PCR reaction to produce ds DNA that runs from NsiI to BstEII. The primers are identical to the 5xe2x80x2 ends of the synthetic bits shown and of length 21 for the first and 17 for the second. As the variability is very high, we would endeavor to obtain between 108 and 109 transformants (the more the better).
Proteins of this invention may be produced by any conventional technique, including
a) nonbiological synthesis by sequential coupling of components, e.g. amino acids,
b) production by recombinant DNA techniques in suitable host cells, and
c) semisynthesis, for example, by removal of undesired sequences from LACI-K1 and coupling of synthetic replacement sequences.
Proteins disclosed herein are preferably produced, recombinantly, in a suitable host, such as bacteria from the genera Bacillus, Escherichia, Salmonella, Erwinia, and yeasts from the genera Hansenula, Kluyveromyces, Pichia, Rhinosporidium, Saccharomyces, and Schizosaccharomyces, or cultured mammalian cells such as COS-1. The more preferred hosts are microorganisms of the species Pichia pastoris, Bacillus subtilis, Bacillus brevis, Saccharomyces cerevisiae, Escherichia coli and Yarrowia lipolytica. Any promoter which is functional in the host cell may be used to control gene expression.
Preferably the proteins are secreted and, most preferably, are obtained from conditioned medium. Secretion is the preferred route because proteins are more likely to fold correctly and can be produced in conditioned medium with few contaminants. Secretion is not required.
Unless there is a specific reason to include glycogroups, we prefer proteins designed to lack N-linked glycosylation sites to reduce potential for antigenicity of glycogroups and so that equivalent proteins can be expressed in a wide variety of organisms including: 1) E. coli, 2) B. subtilis, 3) P. pastoris, 4) S. cerevisiae, and 5) mammalian cells.
Several means exist for reducing the problem of host cells producing proteases that degrade the recombinant product; see, inter alia BANE90 and BANE9 1. VAND92 reports that overexpression of the B. subtilis signal peptidase in E. coli. leads to increased expression of a heterologous fusion protein. ANBA88 reports that addition of PMSF (a serine proteases inhibitor) to the culture medium improved the yield of a fusion protein.
Other factors that may affect production of these and other proteins disclosed herein include: 1) codon usage (optimizing codons for the host is preferred), 2) signal sequence, 3) amino-acid sequence at intended processing sites, presence and localization of processing enzymes, deletion, mutation, or inhibition of various enzymes that might alter or degrade the engineered product and mutations that make the host more permissive in secretion (permissive secretion hosts are preferred).
Reference works on the general principles of recombinant DNA technology include Watson et al., Molecular Biology of the Gene, Volumes I and II, The Benjamin/Cummings Publishing Company, Inc., Menlo Park, Calif. (1987); Darnell et al., Molecular Cell Biology, Scientific American Books, Inc., New York, N.Y. (1986); Lewin, Genes II, John Wiley and Sons, New York, N.Y. (1985); Old, et al., Principles of Gene Manipulation: An Introduction to Genetic Engineering, 2d edition, University of California Press, Berkeley, Calif. (1981); Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Hair, N.Y. (1989); and Ausubel et al, Current Protocols in Molecular Biology, Wiley Interscience, NY, (1987, 1992). These references are herein entirely incorporated by reference as are the references cited therein.
Any suitable method may be used to test the compounds of this invention. Scatchard (Ann NY Acad Sci (1949) 51:660-669) described a classical method of measuring and analyzing binding which is applicable to protein binding. This method requires relatively pure protein and the ability to distinguish bound protein from unbound.
A second appropriate method of measuring Kd is to measure the inhibitory activity against the enzyme. If the Kd to be measured is in the 1 nM to 1 xcexcM range, this method requires chromogenic or fluorogenic substrates and tens of micrograms to milligrams of relatively pure inhibitor. For the proteins of this invention, having KD in the range 5 nM to 50 pM, nanograms to micrograms of inhibitor suffice. When using this method, the competition between the inhibitor and the enzyme substrate can give a measured Ki that is higher than the true Ki. Measurement reported here are not so corrected because the correction would be very small and the any correction would reduce the Ki. Here, we use the measured Ki as a direct measure of KD.
A third method of determining the affinity of a protein for a second material is to have the protein displayed on a genetic package, such as M13, and measure the ability of the protein to adhere to the immobilized xe2x80x9csecond materialxe2x80x9d. This method is highly sensitive because the genetic packages can be amplified. We obtain at least semiquantitative values for the binding constants by use of a pH step gradient. Inhibitors of known affinity for the protease are used to establish standard profiles against which other phage-displayed inhibitors are judged. Any other suitable method of measuring protein binding may be used.
Preferably, the proteins of this invention have a KD for plasmin of at most about 5nM, more preferably at most about 300 pM, and most preferably 100 pM or less. Preferably, the binding is inhibitory so that Ki is the same as KD. The Ki of QS4 for plasmin is about 2nM. The Ki of SPI11 for plasmin is about 88 pM.
The preferred subject of this invention is a mammal. The invention is particularly useful in the treatment of humans, but is suitable for veternary applications too.
Herein, xe2x80x9cprotectionxe2x80x9d includes xe2x80x9cpreventionxe2x80x9d, xe2x80x9csuppressionxe2x80x9d, and xe2x80x9ctreatmentxe2x80x9d. xe2x80x9cPreventionxe2x80x9d involves administration of drug prior to the induction of disease. xe2x80x9cSuppressionxe2x80x9d involves administration of drug prior to the clinical appearance of disease. xe2x80x9cTreatmentxe2x80x9d involves administration of drug after the appearance of disease.
In human and veterinary medicine, it may not be possible to distinguish between xe2x80x9cpreventingxe2x80x9d and xe2x80x9csuppressingxe2x80x9d since the inductive event(s) may be unknown or latent, or the patient is not ascertained until after the occurrence of the inductive event(s). We use the term xe2x80x9cprophylaxisxe2x80x9d as distinct from xe2x80x9ctreatmentxe2x80x9d to encompass xe2x80x9cpreventingxe2x80x9d and xe2x80x9csuppressingxe2x80x9d. Herein, xe2x80x9cprotectionxe2x80x9d includes xe2x80x9cprophylaxisxe2x80x9d. Protection need not by absolute to be useful.
Proteins of this invention may be administered, by any means, systemically or topically, to protect a subject against a disease or adverse condition. For example, administration of such a composition may be by any parenteral route, by bolus injection or by gradual perfusion. Alternatively, or concurrently, administration may be by the oral route. A suitable regimen comprises administration of an effective amount of the protein, administered as a single dose or as several doses over a period of hours, days, months, or years.
The suitable dosage of a protein of this invention may depend on the age, sex, health, and weight of the recipient, kind of concurrent treatment, if any, frequency of treatment, and the desired effect. However, the most preferred dosage can be tailored to the individual subject, as is understood and determinable by one of skill in the art, without undue experimentation by adjustment of the dose in ways known in the art.
For methods of preclinical and clinical testing of drugs, including proteins, see, e.g., Berkow et al, eds., The Merck Manual, 15th edition, Merck and Co., Rahway, N.J., 1987; Goodman et al, eds., Goodman and Gilman""s The Pharmacological Basis of Therapeutics, 8th edition, Pergamon Press, Inc., Elmsford, N.Y., (1990); Avery""s Drug Treatment: Principles and Practice of Clinical Pharmacology and Therapeutics, 3rd edition, ADIS Press, LTD., Williams and Wilkins, Baltimore, Md. (1987), Ebadi, Pharmacology, Little, Brown and Co., Boston, (1985), which references and references cited there are hereby incorporated by reference.
In addition to a protein here disclosed, a pharmaceutical composition may contain pharmaceutically acceptable carriers, excipients, or auxiliaries. See, e.g., Berker, supra, Goodman, supra, Avery, supra and Ebadi, supra.
Proteins of this invention may be applied in vitro to any suitable sample that might contain plasmin to measure the plasmin present. To do so, the assay must include a Signal Producing System (SPS) providing a detectable signal that depends on the amount of plasmin present. The signal may be detected visually or instrumentally. Possible signals include production of colored, fluorescent, or luminescent products, alteration of the characteristics of absorption or emission of radiation by an assay component or product, and precipitation or agglutination of a component or product.
The component of the SPS most intimately associated with the diagnostic reagent is called the xe2x80x9clabelxe2x80x9d. A label may be, e.g., a radioisotope, a fluorophore, an enzyme, a co-enzyme, an enzyme substrate, an electron-dense compound, or an agglutinable particle. A radioactive isotope can be detected by use of, for example, a xcex3 counter or a scintillation counter or by autoradiography. Isotopes which are particularly useful are 3H, 125I, 131I, 35S, 14C, and, preferably, 125I. It is also possible to label a compound with a fluorescent compound. When the fluorescently labeled compound is exposed to light of the proper wave length, its presence can be detected. Among the most commonly used fluorescent labelling compounds are fluorescein isothiocyanate, rhodamine, phycoerythrin, phycocyanin, allophycocyanin, o-phthaldehyde, and fluorescamine. Alternatively, fluorescence-emitting metals, such as 125Eu or other lanthanide, may be attached to the binding protein using such metal chelating groups as diethylenetriaminepentaacetic acid or ethylenediamine-tetraacetic acid. The proteins also can be detectably labeled by coupling to a chemiluminescent compound, such as luminol, isolumino, theromatic acridinium ester, imidazole, acridinium salt, and oxalate ester. Likewise, a bioluminescent compound, such as luciferin, luciferase and aequorin, may be used to label the binding protein. The presence of a bioluminescent protein is determined by detecting the presence of luminescence. Enzyme labels, such as horseradish peroxidase and alkaline phosphatase, are preferred.
There are two basic types of assays: heterogeneous and homogeneous. In heterogeneous assays, binding of the affinity molecule to analyte does not affect the label; thus, to determine the amount of analyte, bound label must be separated from free label. In homogeneous assays, the interaction does affect the activity of the label, and analyte can be measured without separation.
In general, a plasmin-binding protein (PBP) may be used diagnostically in the same way that an antiplasmin antibody is used. Thus, depending on the assay format, it may be used to assay plasmin, or, by competitive inhibition, other substances which blind plasmin.
The sample will normally be a biological fluid, such as blood, urine, lymph, semen, milk, or cerebrospinal fluid, or a derivative thereof, or a biological tissue, e.g., a tissue section or homogenate. The sample could be anything. If the sample is a biological fluid or tissue, it may be taken from a human or other mammal, vertebrate or animal, or from a plant. The preferred sample is blood, or a fraction or derivative thereof.
In one embodiment, the plasmin-binding protein (PBP) is immobilized, and plasmin in the sample is allowed to compete with a known quantity of a labeled or specifically labelable plasmin analogue. The xe2x80x9cplasmin analoguexe2x80x9d is a molecule capable of competing with plasmin for binding to the PBP, which includes plasmin itself. It may be labeled already, or it may be labeled subsequently by specifically binding the label to a moiety differentiating the plasmin analogue from plasmin The phases are separated, and the labeled plasmin analogue in one phase is quantified.
In a xe2x80x9csandwich assayxe2x80x9d, both an insolubilized plasmin-binding agent (PBA), and a labeled PBA are employed. The plasmin analyte is captured by the insolubilized PBA and is tagged by the labeled PBA, forming a tertiary complex. The reagents may be added to the sample in any order. The PBAs may be the same or different, and only one PBA need be a PBP according to this invention (the other may be, e.g., an antibody). The amount of labeled PBA in the tertiary complex is directly proportional to the amount of plasmin in the sample.
The two embodiments described above are both heterogeneous assays. A homogeneous assay requires only that the label be affected by the binding of the PBP to plasmin. The plasmin analyte may act as its own label if a plasmin inhibitor is used as a diagnostic reagent.
A label may be conjugated, directly or indirectly (e.g., through a labeled anti-PBP antibody), covalently (e.g., with SPDP) or noncovalently, to the plasmin-binding protein, to produce a diagnostic reagent. Similarly, the plasmin binding protein may be conjugated to a solid phase support to form a solid phase (xe2x80x9ccapturexe2x80x9d) diagnostic reagent. Suitable supports include glass, polystyrene, polypropylene, polyethylene, dextran, nylon, amylases, and magnetite. The carrier can be soluble to some extent or insoluble for the purposes of this invention. The support material may have any structure so long as the coupled molecule is capable of binding plasmin.
A Kunitz domain that binds very tightly to plasmin can be used for in vivo imaging. Diagnostic imaging of disease foci was considered one of the largest commercial opportunities for monoclonal antibodies, but this opportunity has not been achieved. Despite considerable effort, only two monoclonal antibody-based imaging agents have been approved. The disappointing results obtained with monoclonal antibodies is due in large measure to:
i) Inadequate affinity and/or specificity;
ii) Poor penetration to target sites;
iii) Slow clearance from nontarget sites;
iv) Immunogenicity (most are murine); and
v) High production cost and poor stability.
These limitations have led most in the diagnostic imaging field to begin to develop peptide-based imaging agents. While potentially solving the problems of poor penetration and slow clearance, peptide-based imaging agents are unlikely to possess adequate affinity, specificity and in vivo stability to be useful in most applications.
Engineered proteins are uniquely suited to the requirements for an imaging agent. In particular the extraordinary affinity and specificity that is obtainable by engineering small, stable, human-origin protein domains having known ill vivo clearance rates and mechanisms combine to provide earlier, more reliable results, less toxicity/side effects, lower production and storage cost, and greater convenience of label preparation. Indeed, it should be possible to achieve the goal of realtime imaging with engineered protein imaging agents. Plasmin-binding proteins, e.g. SPI 11, may be useful for localizing sites of internal hemorrhage.
Radio-labelled binding protein may be administered to the human or animal subject. Administration is typically by injection, e.g., intravenous or arterial or other means of administration in a quantity sufficient to permit subsequent dynamic and/or static imaging using suitable radio-detecting devices. The dosage is the smallest amount capable of providing a diagnostically effective image, and may be determined by means conventional in the art, using known radio-imaging agents as guides.
Typically, the imaging is carried out on the whole body of the subject, or on that portion of the body or organ relevant to the condition or disease under study. The radio-labelled binding protein has accumulated. The amount of radio-labelled binding protein accumulated at a given point in time in relevant target organs can then be quantified.
A particularly suitable radio-detecting device is a scintillation camera, such as a xcex3 camera. The detection device in the camera senses and records (and optional digitizes) the radioactive decay. Digitized information can be analyzed in any suitable way, many of which are known in the art. For example, a time-activity analysis can illustrate uptake through clearance of the radio-labelled binding protein by the target organs with time.
Various factors are taken into consideration in picking an appropriate radioisotope. The isotope is picked: to allow good quality resolution upon imaging, to be safe for diagnostic use in humans and animals, and, preferably, to have a short half-life so as to decrease the amount of radiation received by the body. The radioisotope used should preferably be pharmacologically inert, and the quantities administered should not have substantial physiological effect. The binding protein may be radio-labelled with different isotopes of iodine, for example 123I, 125I, or 131I (see, for example, U.S. Pat. No. 4,609,725). The amount of labeling must be suitably monitored.
In applications to human subjects, it may be desirable to use radioisotopes other than 125I for labelling to decrease the total dosimetry exposure of the body and to optimize the detectability of the labelled molecule. Considering ready clinical availability for use in humans, preferred radio-labels include: 99mTc, 67Ga, 68Ga, 90Y, 111In, 113mIn, 123I, 186Re, 188Re or 211 At. Radio-labelled protein may be prepared by various methods. These include radio-halogenation by the chloramine-T or lactoperoxidase method and subsequent purification by high pressure liquid chromatography, for example, see Gutkowska et al in xe2x80x9cEndocrinology and Metabolism Clinics of America: (1987) 16 (1):183. Other methods of radio-labelling can be used, such as IODOBEADS(trademark).
A radio-labelled protein may be administered by any means that enables the active agent to reach the agent""s site of action in a mammal. Because proteins are subject to digestion when administered orally, parenteral administration, i.e., intravenous subcutaneous, intramuscular, would ordinarily be used to optimize absorption.
The plasmin-binding proteins of this invention may also be used to purify plasmin from a fluid, e.g., blood. For this purpose, the PBP is preferably immobilized on an insoluble support. Such supports include those already mentioned as useful in preparing solid phase diagnostic reagents.
Proteins can be used as molecular weight markers for reference in the separation or purification of proteins. Proteins may need to be denatured to serve as molecular weight markers. A second general utility for proteins is the use of hydrolyzed protein as a nutrient source. Proteins may also be used to increase the viscosity of a solution.
The protein of this invention may be used for any of the foregoing purposes, as well as for therapeutic and diagnostic purposes as discussed further earlier in this specification.
Chemical polypeptide synthesis is a rapidly evolving area in the art, and methods of solid phase polypeptide synthesis are well-described in the following references, hereby entirely incorporated by reference: (Merrifield, J Amer Chem Soc 85:2149-2154 (1963); Merrifield, Science 232:341-347 (1986); Wade et al., Biopolymers 25:S21-37 (1986); Fields, Int J Polypeptide Prot Res 35:161 (1990); MilliGen Report Nos. 2 and 2a, Millipore Corporation, Bedford, Mass., 1987) Ausubel el at, supra, and Sambrook el al, supra. Tan and Kaiser (Biochemistry, 1977, 16:1531-41) synthesized BPTI and a homologue eighteen years ago.
As is known in the art, such methods involve blocking or protecting reactive functional groups, such as free amino, carboxyl and thio groups. After polypeptide bond formation, the protective groups are removed. Thus, the addition of each amino acid residue requires several reaction steps for protecting and deprotecting. Current methods utilize solid phase synthesis, wherein the C-terminal amino acid is covalently linked to an insoluble resin particles that can be filtered. Reactants are removed by washing the resin particles with appropriate solvents using an automated machine. Various methods, including the xe2x80x9ctbocxe2x80x9d method and the xe2x80x9cFmocxe2x80x9d method are well known in the art. See, inter alia, Atherton et al., J Chem Soc Perkin Trans 1 :538-546 (1981) and Sheppard el al., Int J Polypeptide Prot Res 20:451-454 (1982).